Electrodeposition of nickel



Patented June 1946 Henry Brown, Detroit, Mich, mini); to The Udylite Corporation, Detroit, Mich" a corporation of Delaware No Drawing. Application August 27, 1942,

, Serial No. 456,362

This invention relates to the electrodeposition of nickel from an aqueous acid bath.

The object of this invention is the electrodeposition, of brilliant, highly lustrous ductile nickel plate having good bond to the basis metal. This object can be achieved by using a salt of the metal thallium, such as thallium sulfate, in an aqueous acid nickel bath together with an organic compound containing the linkage,

(an unsaturated carbon atom connected to a positive valent'sulfur atom), as illustrated by the aryl sulfonamidcs, aryl sulfonates, aryl sulflnates, etc. (see Table I) Tut: I

The most eflective type 0] compounds Optimum cone. in bath, g./l. o-Benzoic sulfimide '1-3' Benzene disulfonamide 0.25-1.0. Benzene sulfonamide 1-3 o-Toluene sulfonamide a- 1-2 p-Toluene sulfonamide 1-2.5 Diphenyl sulfone sulfonic acid 3 Naphthalene 1,5-disulfonic acid 3 Benzene m-disulfonic acid Benzene sulfinic acid .l-1.0 p-Toluene'sulilnic acid; .1-1.0

The combination of these brightening addition agents can best be used in the acid nickel baths of the Watts type and its modifications, using formates, citrates, etc., as well as boric acid as buifers. The most suitable nickel plating baths and their temperatures and preferred hydrogen ion concentration are given in Table 11. Small concentrations of citric acid especially, and also of formic, can often be used with the boric with benefit. At the higher temperatures, it is better to use the lower pH values. Nickel sulfamate can be used in concentrations up to saturation toreplace the nickel sulfate.

Any thallous (11+) salt soluble in the bath can be used, as for example, thallium sulfate, thallium chloride, thallium fluoride, thallium carbonate 6 Claims. (01. 204-43) and thallium hydroxide; the important thing is that in introducing the thallous ion into the bath, it is not desirable to introduce any harmful anion such as the nitrate ion into the nickel plating bath. The thallium is usually added to the bath in the form of thallium sulfate (T12SO4), as this is about the most readily available salt. In a warm Watts type of nickel bath, thallium sulfate alone in concentration of about 1 gram per liter and less brightens, in the high current density areas, e. g. 30 amps. per sq. ft. and higher, but the lower current densities are darkish. By increasing the concentration, the dark plate forming at the low current density areas, e. g. 5 amps. per sq. ft., extends to the higher current density areas. Lowering the pH tends to decrease this eflect, the thallium ion acting like the zinc ion and somewhat (though to a slighter extent) like the copper ion in the nickel bath in this respect. When, however, a

=c-s0- I type of compound (see Table I) such as saccharin or p-toluene sulfonamide, or 1,5-naphthalene disulfonic acid, is also added to the warm acid nickel bath containing the thallium sulfate, a brilliant, very ductile plate, having good bond to the basis metal, is obtained. That is, not only is the plate made brighter and over a wider current density range, but also the bond and ductility of the plate are improved. These organic compounds, thus, not only increase the tolerance of the bath to the thallium ion but also greatly enhance the brightness obtained.

Thus, on the addition of 1 gram per liter or less of thallium sulfate and 1.5 grams per liter of o-benzoyl suliimide and l'gram per liter of p-toluene sulfonamide to an acid nickel bath such as those listed in Table II. a brilliant, ductile plate is obtained over the entire plate except the lowest current density areas (e. g. 3 amps. per sq. ft. or less) which are white rather than brilliant. If the pH is too high, this white area extends to the higher current density areas. The thallium now acts very much like zinc and cadmium in the nickel bath (and not like copper). Too high concentration of thallium, like that of zinc and cadmium, causes the plate to be exceedingly brilliant but too hard and brittle and also makes the recesses dark; however, at optimum concentrations, the plate is both ductile and bright with a very good rate of brightening. A plate of .0005"-.001" of such nickel will have a brilliant luster even when plated over steel ilnished with a final grease emery. The best used with small amounts brightene'r.

pH values are from 2.5 to 4.5 at a temperature of about 50 C., with the widest bright plating range at the lower pH values. The presence of ammonium salts are not desirable, especially in warm baths, as they decreasethe ductility of the plate. In cold baths, a greater concentration of ammonium salts can be tolerated and less thallium must be used. Sodium, and es cially magnesium salts, are not nearly as cri lcal but in general, it is preferred not to have much of such salts present. I

The optimum concentration range for the thallium ion is from .24 g./l. to 1.6 g./l. depending on such conditions as pH of the bath, temperature, and the particular V =c-socompounds used. Thus, where the thallium ion is obtained from dissolving T12804- in the bath, the concentrations of thallium sulfate to be used with the compounds (Table I) is from 0.3 gram per liter to even 2 grams per liter depending on such conditions as the pH of the bath, temperature and the exact compounds used, etc. Also, if another brightener such as an unsaturated organic compound is also used in conjunction with the thallium and the I ;io compounds, the concentrations of thallium must always be less than with the compounds present, or else the plate will be of poor color and bond (unless, of course, the purpose is to obtain dark plate). In barrel plating even the cold double ammonium salt bath can be of thallium alone as The *o compounds listed in Table I are not the only compounds that show the beneficial eflects with the thallium ion but others also do, though they are not as effective, for example, benzene sulfonic acid (in large concentration), p-brom benzene sulfonic acid, diphenyl sulfonic acid, p-diphenyl benzene sulfonic acid and the naphthalene sulfonic acids.

The aryl sulflnic acids (containing the 4 group) e. g. benzene or toluene sulflnates are even more eflective than the aryl suli'onamides and aryl sulionates (containing the v 3SOr compounds. A very useful application or the sulfinic acids would be if by accident too much T1+ is added to a bath, the addition of even a small amount (.1 g./l. or less) of the sulflnate will counteract the harmful eifects immediately.

If certain substituting groups are present on the aryl ring, the beneficial effects produced by the I =o-so compounds will be minimized or even completely overshadowed; for example, hydroxy groups on the ring, nitro groups, amine groups and too many alkyl groups on the ring which introduces insolubility and colloidality. The hydroxy groups decrease the brightness but do not affect the ductility. The nitro groups on the ring tendto.

make the plate less ductile. An amine group on the ring in the case of a sulfonamide as with p-amino benzene sulfonamide completely nullifies its beneficial properties in that the plate produced by this compound is dark, fine-grained and brittle which the addition of o-benzoyl sulilmide does not remedy. On the other hand, theharmful effect 01' an amine group on the ring of an aryl sulfonic acid is greatly decreased through.

inner salt formation. However, where the amine groups exceed the sulfonic, then brittle grey plate is obtained as with 2,5-diamino benzene suli'onic acid. Also, p-nitro aniline o-sulfonic acid gives grey brittle plate.

The uniqueness of the group to negative valent sulfur, and the mechanism oi. its deposition. That the mechanism of the reduction is not necessarily of the simplest form is indicated by the fact that with s-naphthalene sulfonamide as the only organic compound in the bath, not only is the odor of naphthalene apparent at the cathode during the plating, but the analysis of the plate shows the presence of carbon as well as sulfur.

It seems that the process involving the reduction and hydrogenolysis or the sulfur of the positive valent compounds to a negative valence produces. in part at least, an inhibitor or poison of the nickel (as catalyst in perhaps many cases) in the reduction of (or addition of electrons to) Tl+ (and other active ions or active unsaturated organic materials). Hence, the plating bath is made more tolerant to larger concentrations of these active substances (see United 'States Patent 2,191,813). That is, the plating bath is made more tolerant to these substances because they are less easily reduced in the presence. of the hill)- compounds. The

=t io compounds thus regulate to varying extents the reduction or such active substance as T1 (and other active inorganic and organic materials) in the nickel bath. The difference in degree of eifectiveness of the various =i o compounds would seemto depend on the exact inhibitor formed and its amount and on its own particular eflect on the nickel plate.

The aryl sulflnic acids are evidently more easily reduced than the aryl sulfonamides and sul-- The use of a wetting agent to prevent pitting,

without materially affecting the brightness is desirable in baths using Tl+ and =i io compounds. Also, it is important to use the proper type of rubber in any rubber-lined tanks or other equipment used in contact with this type of plating solution or at least to check an unknown type for its eifect on the plate.

I claim:

1. A bath for electrodepositing ductile bright nickel plate comprising an aqueous acid nickel solution comprising essentially amaterial selected from the group consisting of nickel sulfate, nickel chloride, a mixture of nickel sulfamate and nickel chloride, a mixture of nickel sulfamate, nickel chloride and nickel sulfate, and a mixture of nickel sulfate and nickel chloride, said solution having dissolved therein thallium sulfate in an amount falling within a range of from .1 gram per liter to 2 grams per liter and an aryl organic compound containing the group where the sulfur is positive valent and attached to at least one oxygen radical. the said bath having a pH falling within a range of from 2.5 to 4.5.

2. A bath for electrodepositing ductile bright 6 nickel sulfate and nickel chloride, said solution having dissolved therein thallium sulfate in an amount falling within a range of from .1 gram per liter to 2 grams per liter and an aryl organic compound containing the group where the sulfur is positive valent and attached to at least one oxygen radical. the said bath having a pH falling within a range of from 2.5 to 4.5 at a temperature of about 50 C.

3. The method of electrodepositing nickel comprising electrodepositing nickel from an aqueous acid nickel solution comprising essentially a material selected from the group consisting of nickel sulfate. nickel chloride, a mixture of nickel sulfamate and nickel chloride, a mixture of nickel sulfamate, nickel chloride and nickel sulfate, and a mixture of nickel sulfate and nickel chloride, said solution having thallium sulfate dissolved therein in an amount falling within a range of from .1 gram per liter to 2 grams per liter, the

said bath having a pH falling within a range of from 2.5 to 4.5

4. The method of electrodepositlng nickel comprising electrodepositing nickel from an aqueous acid nickel solution comprising essentially a material selected from th group consisting of nickel sulfate, nickel chloride, a mixture of nickel sulfamate and nickel chloride, a mixture of nickel sulfamate, nickel chloride and nickel sulfate, and a mixture of nickel sulfateand nickel chloride, said solution having dissolved therein thallium sulfate in an amount falling within a range of from .1 gram per liter to 2 grams per liter and an aryl organic compound containing the group where the sulfur is positive valent and attached to at least one oxysen radical, the said bath havterial selected from the group consisting of nickel sulfate, nickel chloride, a mixture of nickel sulfamate and nickel chloride, a mixture of nickel sulfamate, nickel chloride and nickel sulfate, and

nickel platecomprising an aqueous acid nickel solution comprising essentially a material selected from the group consisting of nickel sulfate, nickel chloride, a mixture of nickel sulfamaie and nickel chloride, a mixture of nickel sulfamate, nickel chloride andnickelsulfataandamixtureot a mixture of nickel sulfate and nickel chloride, said solution having dissolved therein thallium sulfate in an amount falling within arange of from .lgrampe'rlitertoilgramsperliterand anaryl organic compound containing the group n un consisting 0! nickel sulfate, nickel chloride, nickel sulfamate, a mixture of nickel sulfamate and nickel chloride, a mixture of nickel sulfamate, nickel chloride and nickel sulfate, and a mixture of nickel sulfate and nickel chloride, said solution having thallium sulfate unsolved therein in an amountfallingwithinarangeoffromaboutd gramperliterto2gramsperliter.

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